Bacteriohopanepolyols preserved in silica sinters from Champagne Pool (New Zealand) indicate a declining temperature gradient over the lifetime of the vent

Abstract

Siliceous sinters from Champagne Pool (CP), a geothermal vent in the Taupo Volcanic Zone, North Island, New Zealand contained exceptionally well-preserved bacteriohopanepolyol (BHP) distributions. BHPs were present in a range of sinters deposited over the lifetime of CP (900 yr before present). The distributions correlated well with the presence of members of BHP-producing bacterial orders known to inhabit CP. For example, Acidothiobacillales, Burkholderiales and Pseudomonadales are known sources of composite BHPs (with a more complex functional group at C-35), such as bacteriohopanetetrol cyclitol ether, found in high relative abundance in each CP sinter analysed. The BHP distributions preserved in CP sinters were different from those described previously for any other environmental setting, with pentafunctionalised BHPs accounting for up to 55% of the total assemblage. Furthermore, composite BHPs were the most abundant compound type in each sample and accounted for up to 80% of the total BHP distribution. As the age of sinter increased a general increase in BHP abundance was observed. Similarly, in older sinters the complexity of the BHP compounds increased. The observations are consistent with a higher temperature of vent water in the past. The excellent preservation of BHPs in this setting, over the lifetime of the vent, highlights the usefulness of BHPs as biomarkers for reconstructing modern and ancient geothermal vent bacterial communities.